The present invention relates to a breather device of an automatic transmission.
In general, an automatic transmission that is mounted on a vehicle accommodates a power transmission mechanism portion formed by a torque converter, a speed change mechanism, and the like, in a case storing ATF (automatic transmission fluid) serving as hydraulic fluid and lubricating oil. Such a case is usually provided with a breather device that prevents the case from being damaged by an excessive load that is applied to the case when the pressure in the case increases due to an increase in oil pressure, for example.
The breather device has a breather chamber capable of communicating the case with the atmosphere. For example, when the pressure in the case exceeds the pressure outside the case, air in the case is discharged into the atmosphere through the breather chamber to eliminate the pressure difference between the inside and outside of the case. A breather device described in Japanese Utility Model Application Publication No. JP-A-H2-94963, for example, is known as such a breather device.
The breather device of Japanese Utility Model Application Publication No. JP-A-H2-94963 includes an oil chamber (i.e., a main body) that is attached to the upper side of a case. The oil chamber has an inlet passage that provides communication between the oil chamber and the case, an oil return passage that provides communication between the oil chamber and the case at a different location from the inlet passage, and a breather (i.e., an outlet passage) that provides communication between the inside and outside of the oil chamber at a different location from the inlet passage and the oil return passage.
High pressure air that has flowed into the oil chamber through the inlet passage is discharged to the outside of the oil chamber through the breather (the outlet passage), while ATF that has flowed into the oil chamber through the inlet passage with the high pressure air is returned into the case through the oil return passage.